Four Types of Evidence for Chemical Reactions

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Transcript of Four Types of Evidence for Chemical Reactions

Four Evidences for Chemical Reactions Julia Swanson 8-1/3 Color Change Color changes occur when different combinations of molecules reflect light differentlyThe forming of new bonds influences the energy of the electrons, which then influences the color of the substancesExample: Blue litmus paper turns red when placed in acid. The Four Types of Evidence Are: Formation of a precipitateFormation of a gasColor ChangeEnergy Change Chemical Reactions Chemical reactions involve a rearrangement of atoms or ions through the breaking and forming of bonds to create new and different substances. Formation of a Precipitate A precipitate forms when a new substance is formed with a much lower solubility than the original substance. A solid is formed from a mixture of solutionsExample: When aqueous silver nitrate (AgNO3) is added to a solution containing potassium chloride (KCl), the precipitation of a white solid, silver chloride (AgCl), is observed. Formation of a Gas Visible bubbles without boiling usually indicate the formation of a gasWhen gas is produced, it shows an increase in kinetic energy of the atom (compound) as it is changed to a gasExample: Antacid tablets in water release carbon dioxide gas Energy Change New substances that form contain a different amount of chemical energy than the reactantsHeat and/or light is released or absorbed, following the Law of Conservation of EnergyMost release energy to their surroundings, heating the container and air around the reaction, but a few absorb energy cooling their surroundingsExample: the combustion of gasoline Chemical Reactions Since this forming of bonds cannot be directly observed, there are certain things to look for that help identify if a chemical reaction has taken place. These clues are the evidences of chemical reactions. References http://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3Adc5f2bcb89346020bd8327fb5b5fa5e4da3d0b70d7ba0071bc170bb2%2BIMAGE%2BIMAGE.1 http://www.dcr.virginia.gov/grassroots/images/index1004_gr1004maglass.jpg http://img.ehowcdn.com/article-new/ds-photo/getty/article/165/70/80406866_XS.jpg http://students.cis.uab.edu/ash13y/Precipitate.jpg http://revision-systems.co.uk/wp-content/uploads/2013/01/FoamingBeakerCartoon.jpg http://0.tqn.com/d/chemistry/1/0/P/n/litmuspaper.jpg http://olmcwikidlinks.wikispaces.com/file/view/chemical_change.jpg/235027574/chemical_change.jpg http://cdn.c.photoshelter.com/img-get/I0000zAOrtJlOsfA/s/860/860/Fphoto-67331207C-6ES.jpg http://www.buzzle.com/img/articleImages/512528-39412-57.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/7/78/Chemical_precipitation_diagram.svg/220px-Chemical_precipitation_diagram.svg.png http://sites.jmu.edu/chemdemo/files/2011/06/100_3448-200x150.jpg